Heretofore the detection of lithium in animal organs has been achieved only by post mortem specimens preferred in-vivo. This type of study of lithium level in different tissues and particularly in the brain is reported in 1976 by M. A. Spirites in "Pharmaceutical Biochemistry and Behavior", Volume 5, pages 143 to 147 and in 1980 by M. Thellier et al., in "Nature", Volume 283, pages 299 to 302. In view of use of lithium clinically for the treatment of mania and its effect on attenuation of manic and depressive episodes, it is important to be able to measure in-vivo the amount of lithium in body tissues and organs (in particular the brain and kidney).
Because of long term clinical administration of lithium salts and side effects, it is essential to monitor the action on the brain and any possible kidney overload or damage.
In connection with in-vivo measurements of humans there are many problems to be resolved to find a method that is acceptable as a procedural measure, particularly in view of low concentrations of lithium in the form of lithium salts resident in the body, the sensitiveness of the brain area, the inability to take specimens, etc. Also the accuracy of measurement of small concentrations of the lithium without serious interruption of life processes and thus necessarily by indirect methods presents another set of problems. Furthermore, the time it takes to ascertain the measurements is critical, in order to make them relate to the clinical effects and to investigate adequacy of doses, etc.
Thus, the objectives of this invention are to resolve the foregoing problems and to provide an in-vivo measurement of lithium concentrations in particularly the human body with enough accuracy to advance the clinical and therapeutic usage thereof.
The determination of lithium in various materials by the neutron activation method using the .sup.6 Li(n,.alpha.)T reaction has been reported by B. P. Zverev et al., in Soviet Atomic Energy (U.S.A.), Vol. 32, No. 1, Jan. 1972, pp. 35-37. H. I. Kallmann et al., 2,288,717 --July 7, 1942 also teaches liberation of tritium from lithium isotopes by neutron irradiation for forming images to thus show the nature of the neutron beam irradiation pattern.
However, there is no known method of in-vivo determination of lithium present in animal tissues and organs prior to this invention.